Numerical comparison of two different tibial nails: expert tibial nail and innovative nail

The extended usage of unreamed tibial nailing resulted in reports of an increased rate of complications, especially for the distal portion of the tibia. Unreamed nailing favors biology at the expense of the achievable mechanical stability, it is therefore of interest to define the limits of the clinical indications for this method. Extra-articular fractures of the distal tibial metaphysis, meta-diaphyseal junction, and adjacent diaphysis are distinct in their management from impaction derived “pilon” type fractures and mid-diaphyseal fractures. With this purpose a complete model of the human tibia was realized, simulating a mid-diaphyseal fracture, classified as A2 type 1, according to the AO classification. Two different FE models of nail were developed in order to carry on a mechanical comparison between an innovative design of nail for fractures occurring on long bones and a traditional intra-medullary nail expert tibial nail (DePuy Synthes\(^{\textregistered }\)). The innovative nail’s functioning is based essentially on sliding of conical surfaces, located in a spindle and in holding pins. Spindle and holding pins are connected together by a sleeve. The sliding transforms the rotational and translational motion of the spindle to a radial expansion of the holding pins, protruding inside the intramedullary canal. Results obtained by a non-linear finite element analysis of the models were performed with Abaqus version 5.4 (Hibbitt, Karlsson and Sorensen, Inc., Pawtucket, RI, USA) using the geometric non-linearity and automatic time stepping options. In particular, analyses confirmed a satisfactory behavior of the nail in terms of stress and strain shielding, comparable to the other traditional system of prosthesis. In conclusion, this kind of nail appears to offer a good solution for elderly patients, which could not endure complications due to a complex surgery, as distal or medial screws are not necessary.